An improved form of lid, preferably of a plastic material, for use in lever ring and other kinds of containers, is described in British Appln. No. 8500701 (GB-A-2152913) and has a portion for sealingly engaging with a corresponding portion of a container to which the lid is to be fitted, wherein the lid portion comprises at least one flexible annular fin which extends generally radially outwardly of and circumferentially around the lid and which is arranged to be deformed when the lid is fitted to the container so as to provide sealing engagement between the lid portion and the container portion. The present invention provides a further improvement in lids of such kind and a complementary improvement in such kinds of containers.
The machinery used to put lids on containers is generally arranged to hold each lid in a generally horizontal position and either lower it into the ring of the container by moving it down the vertical axis of the latter or move it generally horizontally across the open top of a container in a slightly tilted attitude, so that a part of the periphery of the lid is abutted against the inside of the lever ring and a downward force is then applied at the opposite part of the periphery of the lid. Although the finned lids according to the aforementioned application are highly effective in sealing the containers to which they are fitted, misalignment can occur in a very small percentage of cases, which causes the fins to be excessively distorted at one part of the lid periphery, so that proper sealing is not achieved, for instance at the opposite part. In other words, the lids occasionally are not located in a generally concentric relationship with the lever rings of the associated containers and not even the natural tendency of the plastic material to achieve a condition of minimum stress is sufficient at times to allow a misaligned lid to centralize itself within the lever ring of the associated container. Misalignment is more likely to occur if the lids are applied by the second of the procedures mentioned or if they suffer damage at the periphery before or during application to the containers.